This invention relates to a vehicle used for transporting freight loads, commonly referred to as a semi-trailer.
For purposes of highway shipment, unit loads of wall board, lumber and the like are routinely placed on a flatbed semi-trailer which in turn is attached to, and supported by a fifth wheel device on a modern truck tractor.
Currently, semi-trailers of the type referred to are primarily constructed of longitudinal and transverse steel support members, attached to and covered by heavy gauge sheet metal flooring or decking sections, resulting in a platform-like upper surface upon which the units loads of freight are loaded.
Normally semi-trailers are loaded by utilizing standard motorized forklift trucks. This type of loading procedure requires dunnage to be placed between the lowest tier of freight and the flatbed semi-trailer platform-like upper surface, as well as between each subsequent tier of freight. The dunnage allows for space in which the fork-like projections of a forklift truck can be maneuvered during loading and unloading operations, as well as providing support for the unit freight loads during transport. In most cases, the dunnage is formed from the same type of material as the freight being transported. This will prevent damage to the freight during transport over rough roadways which would otherwise occur if there were direct contact between the freight and harder surfaces such as steel for example.
The result of the above-described standard semi-trailer construction, combined with the significant amounts of dunnage normally required to properly load a standard 40 foot semi-trailer with freight is a highway vehicle normally having an overall weight in excess of 15 tons, not including the weight of the commodity to be transported.
The fuel expense associated with the operation of such a semi-trailer/truck tractor in addition to the state and federal restrictions on highway vehicle weight have long since created the need for a practical transport vehicle designed to allocate only the minimum amount of weight necessary to the actual vehicle structure itself, and any dunnage required, thus allowing for a maximum amount of freight capacity.
One prior attempt at overall weight reduction design suggested dividing the standard 40 foot length of a semi-trailer into two equal sections, joined together and supported by another series of wheels at the 20 foot point. This design reduced the load requirements of the individual support members and therefore allowed for the use of lighter weight support beams. However, maneuverability of this design proved problematical and positioning the freight to achieve proper weight distribution made loading procedures difficult and time consuming.